19.3 An 8.9-to-21.9GHz Single-Core Oscillator with Reconfigurable Class-F⁻¹ and Enhanced-Colpitts Dual-Mode Operation Achieving 209dBc/Hz FoMT

Emerging needs for incorporating multistandard or software-defined-radio transceivers onto a single chip necessitate oscillator signals with an octave coverage for enabling seamless full-range frequency synthesis. Although most current solutions, particularly in commercial products, rely on configurations that involve multiple oscillators, there is a strong demand for a single LC VCO that provides at least an octave frequency tuning range (FTR) and low phase noise (PN). Recent research has extensively explored multicore multimode operations to substantially extend the FTR of LC VCOs [1-5]. Among key benefits is the improvement in the PN due to the coupling of numerous identical VCO cores, though at the expense of power consumption. Additionally, any explicit loss from mode switching can be circumvented by effectively nullifying the currents flowing through the MOS switches. However, several unavoidable mechanisms can reduce the equivalent quality factor (Q), thus impacting the performance: (1) mismatch between different oscillation cores causes the tanks operation to deviate from their impedance peaks; (2) the use of destructive magnetic coupling in higher-frequency modes decreases the effective inductance, while losses remain nearly unchanged. Furthermore, due to the high complexity and increased constraints in these ultra-wideband VCO circuits, neither the impulse-sensitivity-function (ISF) reshaping based on multiresonance nor the drain-to-gate voltage-gain boosting for noise reduction of transistors have been implemented, as illustrated in Fig. 19.3.1 (top). Consequently, prior-art ultra-wideband VCOs exhibit figure-of-merits (FoMs) of approximately 5 to 10dB inferior to those found in their narrow-band counterparts.